cake mixes are designed to make light fluffy airy cakes just about no matter how bad the baker mangles things. about the only way I can think of to turn a cloud fluffy mix into a brick is mix it up and let it sit on the counter for 4-6 hours before baking.

if you want a dense cake finish, I'd start with some of the ole' fashion recipes - getting a "light" batter in those recipes was very depending on beating / whipping air into the batter.....